Frame structure of a vehicle

ABSTRACT

A frame structure of a vehicle includes a flywheel housing, an intermediate housing and a transmission case that are connected to each other along a longitudinal axis of the vehicle to constitute a vehicle frame with an inner space for accommodating a running-power transmission path for transmitting power from an engine to drive wheels via a HST unit. The flywheel housing has a first end connected to the engine and a second open end opposite to the first end along the longitudinal axis of the vehicle. The intermediate housing has a hollow shape with a first end and a second end located along the longitudinal axis of the vehicle. The first end has an abutting surface against which the second end of the flywheel housing abuts, a support surface located radially inwardly of the abutting surface so as to support the HST unit, and an opening surrounded by the support surface. The opening serves as a first-end opening of the intermediate housing along the longitudinal axis of the vehicle. The abutting surface and the support surface along the longitudinal axis of the vehicle are located so that at least a portion of the HST unit is accommodated within the flywheel housing.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a frame structure of a vehicle that isdesigned to accommodate a running-power transmission mechanism andconstitute at least a part of a vehicle frame.

2. Related Art

A known frame structure as disclosed such as in Japanese PatentApplication Laid-open No. Hei-08-2267 is formed by connection membersmade up of a flywheel housing, an intermediate housing and/or atransmission case that are connected to each other along a longitudinalaxis of the vehicle (hereinafter simply referred to a vehiclelongitudinal axis).

The frame structure of the above type has an insufficient capability ina point as discussed below.

First of all, the frame structure of the above-cited reference includesa front housing (flywheel housing) that accommodates a flywheel and asub-speed change unit, a transmission case connected to the fronthousing and a rear housing connected to the transmission case.Specifically, the front housing has a partition wall formed integraltherewith substantially at the center of the front housing with respectto the vehicle longitudinal axis. The partition wall supports a driveshaft and an intermediate shaft of the sub-speed change unit incooperation with a bearing frame that is connected to a rear side of thefront housing.

According to the above arrangement, the assembling of the framestructure involves troublesome works, which include connecting thebearing frame to the rear side of the front housing while supporting therear ends of the drive shaft and the intermediate shaft on the bearingframe, with the front ends of the drive shaft and the intermediate shaftbeing supported on the partition wall and the other constitutionalmembers of the sub-speed change unit such as a friction clutch beingplaced within the front housing.

Another problem caused by the frame structure of the above-citedreference is that the transmission case is hard to be reduced in sizesince the transmission case, which accommodates a main-speed changeunit, is located in the intermediate position between the front housingand the rear housing. Specifically, in the above-cited reference,transmission shafts (a hollow propeller shaft and a main shaft insertedtherethrough) are disposed coaxially with a crank shaft of the engine,aiming at the reduction of the size of the front housing and the like.However, this arrangement requires the transmission shaft to be locatedwith sufficient distance from a wall of the transmission case to providea space for various transmission members such as gears and clutches tobe mounted on the transmission shafts. Accordingly, a problem in thatthe transmission case is hard to be reduced in size cannot be addressed.

Another problem also lies in an arrangement of the vehicle structure ofthe above-cited reference in a case where a part or all of the innerspace of the vehicle structure is utilized as a hydraulic fluidreservoir tank. Specifically, the hydraulic fluid stored in thereservoir tank is utilized for various hydraulic mechanisms mounted inthe vehicle. Therefore, a sufficient amount of hydraulic fluid must bestored inside of the frame structure in order to avoid fluid running-outfor the hydraulic mechanisms in a case where the frame structure is alsoused as a reservoir tank.

Specifically, variation in position or posture of the vehicle isdirectly reflected in the position or posture of the frame structure,since it constitutes a portion of the vehicle frame. That is, when thevehicle tilts due to such as running up or down a slope, the framestructure takes the same tilting position or posture. In such a tiltingposition or posture, the surface level of stored fluid is changed.Accordingly, fluid running-out for the hydraulic mechanisms is highlylikely to occur when the amount of fluid stored in the reservoir tank issmall. Therefore, it is necessary to store a sufficient amount of fluidinside of the frame structure in a case where the frame structure isalso used as a reservoir tank.

On the other hand, hydraulic fluid stored inside of the frame structuremay cause drag resistance in various transmission mechanisms placedinside of the frame structure. That is, a large amount of fluid storedinside of the frame structure may deteriorate transmission efficiency ofvarious transmission mechanisms that are mounted also inside of theframe structure and hence immersed in the fluid.

Thus, there exist contradictory two demands, one for storing asufficient amount of fluid so as to avoid fluid running out and anotherfor storing a minimum amount of fluid so as to avoid causing resistanceagainst the transmission mechanisms mounted inside of the vehicle frame.The prior frame structure is not designed to fully address thesedemands.

In consideration of the above prior art, it is an object of the presentinvention to provide a frame structure that ensures high efficiencyassembly, while addressing the problems with the interconnectedarrangement of a clutch housing, an intermediate housing and atransmission case along the vehicle longitudinal axis.

It is another object of the present invention to provide a framestructure that ensures high efficiency assembly as well as providing afree space above the intermediate housing, while addressing the problemswith the interconnected arrangement of a clutch housing, an intermediatehousing and a transmission case along the vehicle longitudinal axis.

It is still another object of the present invention to provide a framestructure that is capable of effectively preventing fluid for feeding toa HST unit running-out while keeping the amount of fluid stored in areservoir tank as low as possible, which reservoir tank beingconstituted by at least a portion of an inner space of the framestructure that accommodates a running-power transmission path fortransmitting power from an engine to drive wheels via the HDT unit andis arranged along the vehicle longitudinal axis extending from a firstside to a second side of the vehicle.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided aframe structure of a vehicle that includes a flywheel housing, anintermediate housing and a transmission case that are connected to eachother along a longitudinal axis of the vehicle to constitute a vehicleframe with an inner space for accommodating a running-power transmissionpath for transmitting power from an engine to drive wheels via a HSTunit. The flywheel housing has a first end connected to the engine and asecond open end opposite to the first end along the longitudinal axis ofthe vehicle. The intermediate housing has a hollow shape with a firstend and a second end located along the longitudinal axis of the vehicle,the first end having an abutting surface against which the second end ofthe flywheel housing abuts, a support surface located radially inwardlyof the abutting surface so as to support the HST unit, and an openingsurrounded by the support surface, the opening serving as a first-endopening of the intermediate housing along the longitudinal axis of thevehicle. The abutting surface and the support surface along thelongitudinal axis of the vehicle are located so that at least a portionof the HST unit is accommodated within the flywheel housing.

With the above arrangement, it is possible to easily connect the HSTunit to the support surface of the intermediate housing. Further, theconnection of the intermediate housing to the flywheel housing can bemade after connecting the HST unit to the intermediate housing. As aresult, it is possible to achieve high efficiency assembly.

According to another aspect of the present invention, there is provideda frame structure of a vehicle that includes a flywheel housing, anintermediate housing and a transmission case that are connected to eachother along a longitudinal axis of the vehicle to constitute a vehicleframe with an inner space for accommodating a running-power transmissionpath for transmitting power from an engine to drive wheels via a HSTunit. The flywheel housing has a first abutting surface and a secondabutting surface respectively located closer to a first end and a secondend of the flywheel housing along the longitudinal axis of the vehicle,in which the first abutting surface is connected to the engine, and thesecond abutting surface is connected to the intermediate housing. Thesecond abutting surface has a first opening through which the HST unitcan pass. The flywheel housing has a hollow shape with a center axissubstantially coaxial with a crank shaft of the engine. The intermediatehousing has a hollow body portion and a flange portion. The hollow bodyportion has a first end and a second end, and extending along thelongitudinal axis of the vehicle with a center axis displaced downwardfrom the crank shaft. The flange portion is located closer to the firstend of the hollow body portion, and the flange portion has an opening ina radial center thereof, in which the opening of the flange portionserves as a first-end opening of the intermediate housing along thelongitudinal axis of the vehicle. The flange portion has an abuttingsurface located opposite to the second abutting surface of the flywheelhousing, a support surface located radially inward portion of theabutting surface so as to support the HST unit, and the first-endopening located radially inward of the support surface.

With the above arrangement, it is possible to improve efficiency inmounting the HST unit to the intermediate housing and connecting theintermediate housing to the flywheel housing, while locating a top wallof the intermediate housing as low as possible. Accordingly, it ispossible to mount a step bar or board, which is to be mounted above theintermediate housing, on a lower portion.

In the above arrangement, preferably, the abutting surface and thesupport surface along the longitudinal axis of the vehicle are locatedso that at least a portion of the HST unit is accommodated within theflywheel housing.

In one embodiment, the HST unit includes a pump shaft operativelyconnected to said engine, a hydraulic pump unit driven by the pumpshaft, a hydraulic motor unit for non-stepwisely changing the speed ofdrive power from the engine in cooperation with the hydraulic pump, anoutput shaft rotated by the hydraulic motor unit, and a center sectionsupporting the hydraulic pump unit and the hydraulic motor unit andforming a hydraulic circuit for fluid communication between thehydraulic pump unit and the hydraulic motor unit. The center section isconnected with the support surface of the flange portion so as to sealan inner space of the flywheel housing against the inner space of theintermediate housing in a liquid tight manner.

In the one embodiment, preferably, at least one of the hydraulic pumpunit and the hydraulic motor unit is of a variable displacement typewhose suction/discharge rates are variable by a slanting position of ahydraulic operation type output adjusting member. The hydraulicoperation type output adjusting member is controlled by a switchingvalve in a valve unit provided outside of the flywheel, the intermediatehousing and the transmission case.

Also in the one embodiment, preferably, the center section has a firstside along the longitudinal axis of the vehicle forming a pump supportsurface which supports the hydraulic pump unit, and has a second sidealong the longitudinal axis of the vehicle forming a peripheral edgesurface which abuts against the support surface of the flange portionand forming a motor support surface which is located radially inward ofthe peripheral edge surface and supports the hydraulic motor unit.

More preferably, the pump shaft has a first end along the longitudinalaxis of the vehicle which extends into said flywheel housing so as to beoperatively connected to the driving source, and a second end along thelongitudinal axis of the vehicle which passes through the center sectiontoward the second side of the longitudinal axis of the vehicle. Themotor shaft has a second end along the longitudinal axis of the vehiclewhich extends into said intermediate housing toward the second side ofthe longitudinal axis of the vehicle. A main shaft operatively connectedto the second end of said pump shaft and a propeller shaft operativelyconnected to the second end of said motor shaft are inserted throughsaid intermediate housing along the longitudinal axis of the vehicle.

For example, a center plate may be interposed between the intermediatehousing and the transmission case. The center plate bearing-supports themain shaft and the propeller shaft.

The frame structure may further includes a center plate interposedbetween the intermediate housing and the transmission case so as tobearing-support the main shaft and the transmission shaft.

According to another aspect of the present invention, there is provideda frame structure of a vehicle extending from a first side to a secondside of the vehicle along a longitudinal axis of the vehicle so as toconstitute a vehicle frame as providing an inner space for accommodatinga running-power transmission path for transmitting power from an engineto drive wheels via a HST unit, in which at least a portion of the innerspace defines a hydraulic fluid reservoir space. The hydraulic fluidreservoir space has a partition wall that divides the hydraulic fluidreservoir space into a filter housing portion for accommodating a filterand a main portion other than the filter housing portion. The partitionwall has a communication port for communication between the filterhousing portion and the main portion in a lower region of the hydraulicfluid reservoir space. The filter housing portion is arranged so that atleast hydraulic fluid for replenishing the HST unit is taken out fromthe filter portion.

The thus arranged frame structure is capable of securely gettinghydraulic fluid for the HST unit out of the fluid reservoir space, whilekeeping the amount of hydraulic fluid stored therein as low as possible.Accordingly, it is possible to effectively prevent running-out ofhydraulic fluid for the HST unit during hydraulic fluid is drawn out ofthe frame structure, while preventing deterioration in powertransmission efficiency of power transmission mechanisms placed insideof the frame structure.

Preferably, the partition wall is located so as to have thecommunication hole located substantially at the center of the hydraulicfluid reservoir space with respect to a vehicle width direction. Thisarrangement makes it possible to effectively prevent the fluidrunning-out even when the vehicle makes a turn and tilts rightward orleftward.

Preferably, the partition wall is located so as to have thecommunication hole located substantially at the center of the hydraulicfluid reservoir space with respect to the longitudinal axis of thevehicle. This arrangement makes it possible to effectively prevent thefluid running-out when the vehicle has tilted forward or rearward suchas running up and down a slope.

More preferably, the frame structure is arranged so that an oil heatercan be installed in proximity of the communication hole. Thisarrangement makes it possible to efficiently heat hydraulic fluid drawnout of the frame structure and hence effectively prevent deteriorationin hydraulic effect due to deterioration of the viscosity of hydraulicfluid such as during cold season.

In one embodiment of the another aspect of the present invention, theframe structure includes a flywheel housing, an intermediate housing anda transmission case that are connected to each other along thelongitudinal axis of the vehicle. In this arrangement, the flywheelhousing has a hollow shape with a first end and a second end locatedalong the longitudinal axis of the vehicle. The first end has afirst-end opening and a first-end abutting surface surrounding thefirst-end opening. The second end has a second-end opening and asecond-end abutting surface surrounding the second-end opening. Theintermediate housing has a first end and a second end located along thelongitudinal axis of the vehicle. The first end has an abutting surfaceopposed to the second-end surface of the flywheel housing, a supportsurface located radially inward of the abutting surface so as to supportthe HST unit, and an opening surrounded by the support surface. Theopening of the intermediate housing serves as a first-end opening of theintermediate housing along the longitudinal axis of the vehicle. Thesecond end has an opening serving as a second-end opening of theintermediate housing. The support surface of the intermediate housingand the HST unit supported by the support surface are arranged so as todivide the inner spaces of the flywheel housing, the intermediatehousing and the transmission case into a space of a dry chamber foraccommodating a flywheel and the hydraulic fluid reservoir space.

In the above embodiment, for example, the transmission case has a bulgethat extends in the vehicle width direction as extending from an openingof the first end of the transmission case towards the second end of thetransmission case along the longitudinal axis of the vehicle. The bulgeprovides a space for the filter housing portion so that a filter can beinstalled in place by introducing the same from the first side of thelongitudinal axis of the vehicle.

Alternatively, the transmission case has the filter housing portion on afirst side of the lateral axis of the vehicle at a location from thefirst end opening of the longitudinal axis of the vehicle to the secondend of the longitudinal axis of the vehicle. The intermediate housinghas a recess on the first side of the lateral axis of the vehicle at thesecond end of the intermediate housing along the longitudinal axis ofthe vehicle. The recess is dented toward the second side of the lateralaxis of the vehicle so that a filter can be installed in the filterhousing portion from the first side of the transmission case along thelongitudinal axis of the vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, and other objects, features and advantages of the presentinvention will become apparent from the detailed description thereof inconjunction with the accompanying drawings wherein.

FIG. 1 is a schematic side view of a vehicle, to which the framestructure according to one embodiment of the present invention has beenapplied.

FIG. 2 is a side view of the frame structure of FIG. 1 in longitudinalcross section.

FIG. 3 is an enlarged view of a flywheel housing of the frame structureof FIGS. 1 and 2 in longitudinal cross section.

FIG. 4 is an enlarged view of the flywheel housing of FIG. 3 in lateralcross section.

FIG. 5 is a front side view (a first side view with respect to thelongitudinal axis of the vehicle) of an intermediate housing in theframe structure of FIGS. 1 and 2, with a HST unit removed.

FIG. 6 is a cross sectional view taken along a line VI-VI in FIG. 2,showing a front side view of a part of the HST unit in lateral crosssection.

FIG. 7 is a cross sectional view taken along a line VII-VII in FIG. 2.

FIG. 8 is a cross sectional view taken along a line VIII-VIII in FIG. 4,showing a front side view of a center section in lateral cross section.

FIG. 9 is a side view of a transmission case of the frame structure ofFIGS. 1 and 2 in longitudinal cross section.

FIG. 10 is a cross sectional view taken along a line X-X in FIG. 2,showing a front view of the transmission case in lateral cross section.

FIG. 11 is a cross sectional view taken along a line XI-XI in FIG. 10.

FIG. 12 is a cross sectional view taken along a line XII-XII in FIG. 9.

FIG. 13 is a development plan view of the transmission case in lateralcross section.

FIG. 14 is a hydraulic circuit diagram in one part of the vehicle ofFIG. 1.

FIG. 15 is a hydraulic circuit diagram in another part of the vehicle ofFIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The description will be made for a preferred embodiment of the presentinvention with reference to the accompanied drawings. FIG. 1 is aschematic side view of a working vehicle 1, to which the frame structureof this embodiment has been applied. FIG. 2 is a side view of the framestructure in longitudinal cross section.

As illustrated in FIGS. 1 and 2, a frame structure 100 of thisembodiment constitutes at least a portion of the vehicle frame.Specifically, the frame structure 100 includes a flywheel housing 110connected to an engine 10, an intermediate housing 120 connected to theflywheel housing 110 and a transmission case 130 connected to theintermediate housing 120.

FIGS. 3 and 4 are respectively enlarged side view and plane view of theflywheel housing in longitudinal and lateral cross sections. Asillustrated in FIGS. 1 to 4, the flywheel housing 110 has a first endand a second end along the vehicle longitudinal axis (hereinaftersometimes referred to a first longitudinal end and a second longitudinalend), which ends respectively have a first opening 110 a and a secondopening 110 b, and a hollow shape with a center axis substantiallycoaxial with a crank shaft 11 of the engine. The first opening 110 a issized to allow a flywheel 15, which is operatively connected to theengine 10, to pass therethrough. The second opening 110 b is sized toallow a HST unit 30 (hereinafter described) to pass therethrough. Thefirst end of the flywheel housing 110 is connected to the engine so thatthe flywheel housing 110 is aligned along the vehicle longitudinal axis.

In this embodiment, the engine 10 is located on the front side of thevehicle along the vehicle longitudinal axis. As used throughout thedescription, the first and second longitudinal ends along the vehiclelongitudinal axis respectively represent the front and rear sides of thevehicle and therefore will be replaced with them according to need andcircumstance in the following description. Also, the directional termssuch as forward and rearward are used in reference to the vehiclelongitudinal axis.

The intermediate housing 120 includes a hollow body portion 121extending along the vehicle longitudinal axis and a front flange portion125 located forward of the body portion 121. The front flange portion125 provides a support area for the HST unit 30 as well as an area forconnection with the flywheel housing 110. FIG. 5 is a front side view ofthe intermediate housing with the HST unit 30 removed. FIGS. 6 and 7 arecross sectional views taken along line VI-VI in FIG. 4 and line VII-VIIin FIG. 2 respectively.

Specifically, as illustrated in FIGS. 5 and 6, the front flange portion125 has a forward end (an end faces to the first side of the vehiclelongitudinal axis), of which a radially outward portion forms anabutting surface 125 a that provides an area for connection with theflywheel housing 110.

The abutting surface 125 a is designed to be brought into abutment witha rear end 111 b (an end faces to the second end of the vehiclelongitudinal axis) of the flywheel housing 110. The front flange portion125 has a support surface 125 b located radially inward of the abuttingsurface 125 a of the forward end so as to provide a support area for theHST unit 30.

The front flange portion 125 has an opening 120 a defined or surroundedby the support surface 125 b. The opening 120 a is formed incommunication with a hollow area of the hollow body portion 121 and thusforms a front opening (an opening closer to the first side of thevehicle longitudinal axis) of the intermediate housing

Now, the description will be made for the HST unit 30 supported on thesupport surface 125 b.

As best illustrated in FIGS. 3 and 4, the HST unit 30 includes a pumpshaft 200 whose front end is operatively connected to the engine 10, ahydraulic pump unit 310 which is driven by the pump shaft 200, ahydraulic motor unit 350 which non-stepwisely changes a driving forcefrom the engine in cooperation with the hydraulic pump unit 310, a motorshaft 210 which is rotated by the hydraulic motor unit, and a centersection 380 which supports the hydraulic pump unit and the hydraulicmotor unit and has a hydraulic circuit which communicates the hydraulicpump unit and the hydraulic motor unit with each other so that fluid canflow therebetween.

In the drawings, a reference code 16 is a damper provided on theflywheel 15.

As illustrated in FIGS. 4 and 6, the center section 380 is connected tothe support surface 125 b such as to surround the opening 120 a.

More specifically, the center section 380 has a first side of thevehicle longitudinal axis forming a pump support surface 381 whichsupports the hydraulic motor unit 350, and a second side of the vehiclethe longitudinal axis forming a peripheral edge surface 382 which abutsagainst the support surface 125 b of the flange portion 125 and forminga motor support surface 383 which is located radially inward of theperipheral edge surface 382 to support the hydraulic motor unit 350. Theperipheral edge surface 382 is connected to the support surface 125 b ofthe flange portion 125 so as to close the opening 120 a.

That is, in this embodiment, the center section 380 is connected to thesupport surface 125 b, thereby liquid-tightly separating an inner spacein the flywheel housing 110 from an inner space of the intermediatehousing 120. With this configuration, the inner space in theintermediate housing 120 can be used as an oil chamber, and the innerspace in the flywheel housing 110 can be used as a dry chamber.

FIG. 8 is a sectional view taken along a line VIII-VIII in FIG. 4.

As illustrated in FIG. 8, the center section 380 further includes an oilpassage (a pair of hydraulic lines 385 in this embodiment) whichcommunicates the hydraulic pump unit 310 and the hydraulic motor unit350 such that oil can flow therebetween, and a charge oil passage 386for supplying charge oil into the oil passage 385.

A hydraulic circuit of the frame structure 100 according to thisembodiment including that of the HST unit 30 will be described later.

In this embodiment, the HST unit 30 further includes a pump case 301connected to the pump support surface 381 of the center section 380 suchas to surround the hydraulic pump unit 310, and a motor case 305connected to the motor support surface 383 of the center section 380such as to surround the hydraulic motor unit 350.

The pump shaft 200 is supported by the pump case 301 and the centersection 380 such that the pump shaft 200 can rotate around its axis andsuch that the pump shaft 200 is coaxial with the crank shaft 11 of theengine 10.

More specifically, a front end of the pump shaft 200 extends forwardthrough the pump case 301 such that the front end is operativelyconnected to an output portion 15 a of the flywheel 15, and a rear endof the pump shaft 200 extends rearward through the center section 380such that the rear end is connected to a subsequent transmitting shaft(main shaft 150 in this embodiment).

A front end of the motor shaft 210 is supported by a bearing recessprovided in the center section 380, and a rear end of the motor shaft210 extends rearward through the motor case 305 such that the rear endis connected to a subsequent transmitting shaft (propeller shaft 220 inthis embodiment).

At least one of the hydraulic pump unit 310 and the hydraulic motor unit350 is of a variable displacement type whose suction/discharge rates arevariable by a slanting position of an output adjusting member 313. Bycontrolling the slanting position of the output adjusting member 313,non-stepwisely changed output is obtained from the motor shaft 210 whichis driven by the hydraulic motor unit 350. In this embodiment, thehydraulic pump unit 310 is of a variable displacement type and thehydraulic motor unit 350 is of a fixed displacement type.

The hydraulic pump unit 310 includes a piston unit 311, a cylinder block312 and the output adjusting member 313. As the pump shaft 200 rotates,the piston unit 311 rotates around the axis of the pump shaft 200 andreciprocates in association with the rotation. The cylinder block 312supports the piston unit 311 such that the piston unit 311 canreciprocates. The cylinder block 312 is rotatably and slidably supportedby the pump support surface 381 of the center section 380 with being incommunication with the pair of hydraulic lines 385. The output adjustingmember 313 controls a stroke length of the piston unit 311 according tothe slanting position, and changes the suction/discharge rates by thepiston unit 311.

The variable displacement type hydraulic pump unit 310 further includesa hydraulic operation device 315 (hereinafter described). The slantingposition of the output adjusting member 313 is controlled by thehydraulic operation device 315.

In this embodiment, since the hydraulic pump unit 310 is of an axialpiston type, a movable swash plate is employed as the output adjustingmember 313. If the hydraulic pump unit is of a radial piston type, a camring is employed as the output adjusting member.

The fixed displacement type hydraulic motor unit 320 includes a cylinderblock 322 and a piston unit 321. The cylinder block 322 is rotatably andslidably supported by the motor support surface 383 of the centersection 380 with being in communication with the pair of hydraulic lines385. The piston unit 321 is slidably supported in the cylinder block322. The piston unit 321 reciprocates and rotates by hydraulic pressurefrom the pair of hydraulic line 385 to transmit the rotation to themotor shaft 210.

Thus, in the frame structure 100 of this embodiment, the intermediatehousing 120 has, on its front side, the abutting surface 125 a forabutment with the rear end of the flywheel housing 110, the supportsurface 125 b located radially inward of the abutting surface 125 a tosupport the HST unit 30, and the opening 120 a defined by the supportsurface 125 b to allow the transmission shafts respectively on thedownstream sides of the pump shaft 200 and the motor shaft 210 to passtherethrough.

According to the above arrangement, the HST unit 30 which has beenassembled independently is introduced from the front side of theintermediate housing 120 and connected to the support surface 125 b, andthen the intermediate housing 120 is connected to the flywheel housing110 via the abutting surface 125 a. This achieves ease of connectionbetween the flywheel housing 110 and the intermediate housing 120 withthe HST unit 30 held therein and hence contributes to improved assemblyefficiency.

Preferably, the positions of the abutting surface 125 a and the supportsurface 125 b along the vehicle longitudinal axis are determined so asto allow at least a portion of the HST unit 30 supported on the supportsurface 125 b to be positioned within the flywheel housing 110 in astate with the flywheel housing 110 connected to the intermediatehousing 120.

That is, where the support surface 125 b is located with a greatdistance away from the abutting surface 125 a towards the second side ofthe vehicle longitudinal axis (towards the rear side in thisembodiment), the HST unit 30 is entirely placed in the intermediatehousing 120. This greatly widens the distance between the forward end ofthe intermediate housing 120 a and the support surface 125 b, and hencelowers efficiency in mounting the HST unit 30 to the support surface 125b.

Contrarily to the above, by positioning the abutting surface 125 a andthe support surface 125 b along the vehicle longitudinal axis so that atleast a portion of the HST unit 30 supported on the support surface 125b is positioned within the flywheel housing 110, it is possible toachieve an improved efficiency in mounting the HST unit 30 to thesupport surface 125 b.

In a more preferable arrangement, the support surface 125 b ispositioned at the same level as or forward of the abutting surface 125 aalong the vehicle longitudinal axis. This arrangement can achieve afurther improved efficiency in mounting the HST unit 30.

The frame structure 100 of this embodiment can achieve an improvedefficiency in mounting the HST unit 30 and connecting the flywheelhousing 110 to the intermediate housing 120, as well as securing a freespace above the intermediate housing 120 as much as possible. This pointwill be mentioned in detail below.

As best illustrated in FIG. 2, in this embodiment, while the HST unit 30is accommodated in the flywheel housing 110 and a main-speed change unit40, a PTO clutch unit 70 and the like (hereinafter described) areaccommodated in the transmission case 130, no transmission units such asa speed change mechanism and a clutch mechanism are disposed in theintermediate housing 120. That is, only the transmission shafts such asa main shaft 150 and a propeller shaft 220 respectively connected to thepump shaft 200 and the motor shaft 210 are accommodated in theintermediate housing 120. In this arrangement, there is no need to mountgears, friction plates and the like on the transmission shafts such asthe main shaft 150. Accordingly, the transmission shafts can be locatedin proximity with a wall of the intermediate housing 120.

The above points were taken into account in the frame structure 100 ofthis embodiment. Accordingly, the hollow body portion 121 has a centeraxis displaced downward from a center axis of the flywheel housing 110so as to locate a top wall 121 a of the hollow body portion 121 of theintermediate housing 120 as close as possible to the transmission shaft(the main shaft 150 in this embodiment). The front flange portion 125 ofthe intermediate housing 120 has a lower side located substantially atthe same level as that of the hollow body portion 121, and an upper sidehigher than that of the hollow body portion 121 so as to enable theconnection between the flywheel housing 110 and the hollow body portion121 with their center axes displaced from each other.

That is, as illustrated in FIG. 5, the front flange portion 125 has anupper extension 126 extending from the top wall 121 a of the hollow bodyportion 121 towards the radially outward side or upper side of thehollow body portion 121, a lateral extension 127 extending from alateral wall 121 b of the hollow body portion 121 towards the radiallyouter and inner sides of the hollow body portion 121, and a lowerextension 128 extending from a bottom wall 121 c of the hollow bodyportion 121 towards the radially inner side or upper side of the hollowbody portion 121, so that the abutting surface 125 a located opposite tothe rear end 111 b of the flywheel housing 110, the support surface 125b located radially inward of the abutting surface 125 a to support theHST unit 30, and the front opening 120 a located radially inward of thesupport surface 125 b are respectively defined.

Thus, in the frame structure 100, substantially only the transmissionshaft(s) (the main shaft 150 and the propeller shaft 220 in thisembodiment) is present in the intermediate housing 120, therebydisplacing the axis of the hollow body portion 121 of the intermediatehousing 120 downward from the axis of the flywheel housing 110 so as tolocate the top wall of the hollow body portion 121 as close as possibleto the transmission shaft (the main shaft 150 in this embodiment), andconnecting the flywheel housing 110 by the front flange portion 125 tothe hollow body portion 121 with both axes displaced from each other.

The above arrangement can provide a free space above the hollow bodyportion 121, thereby providing an improved deign flexibility indesigning a vehicle. Particularly, when a step bar or board is to bemounted on the top wall 121 a of the hollow body portion 121 (see FIG.1), it can be mounted as low as possible by the above arrangement,thereby enabling the driver to easily getting on and off the driverseat.

Now, the description will be made for the connection structure betweenthe intermediate housing 120 and the transmission case 130.

FIG. 9 is a side view of the transmission case 130 and its periphery inlongitudinal cross section.

As illustrated in FIG. 9, the intermediate housing 120 includes a rearflange portion 129 located rearward of the hollow body portion 121. Inthis embodiment, the bottom wall 121 c of the hollow body portion 121has a rear end that downwardly bulges to form a downward bulge 122 thatis designed to allow a heater (hereinafter described) to be mountedtherein from the outside (from the front side in this embodiment).

The intermediate housing 120 is separably connected via a center plate18 to the transmission case 130 for accommodating various transmissionmechanisms (hereinafter described). The center plate 18 acts as abearing member for transmission shafts respectively downstream to thepump shaft 200 and the motor shaft 210.

According to the thus arranged frame structure 100 of this embodiment,bearing members, which require complicated manufacturing process to bemanufactured, are formed independently of cast parts, namely theflywheel housing 110, the intermediate housing 120 and the transmissioncase 130, as many as possible, aiming at achieving a simplifiedstructure of the cast parts, namely the flywheel housing 110, theintermediate housing 120 and the transmission case 130, and hencereduction of the manufacturing cost.

That is, in the frame structure 100 of this embodiment, as describedabove, the pump shaft 200 and the motor shaft 210 are respectivelysupported by a corresponding case of the pump case 301 and the motorcase 305, and the center section 380. Further, the transmission shafts150, 200 respectively downstream to the pump shaft 200 and the motorshaft 210 are supported by the center plate 18. Accordingly, it ispossible to reduce the number of downstream processes subjected to theflywheel housing 110, the intermediate housing 120 and the transmissioncase 130 made by casting, such as boring bearing holes, as much aspossible, and hence reduce the manufacturing cost.

Now, the description will be made for the transmission mechanism of thevehicle 1, to which the frame structure 100 of this embodiment has beenapplied. The detailed structure of the transmission case 130 will bedescribed later.

The vehicle 1 has a running-power transmission mechanism fortransmitting power from a power source 10 to the drive wheels, and a PTOtransmission mechanism for transmitting power from the drive source 10to an attached device such as a mower. First, the description will bemade for the running-power transmission mechanism.

The running-power transmission mechanism includes the HST unit 30, thepropeller shaft 220 extending along the vehicle longitudinal axis andconnected to the motor shaft 210 in such a manner to be relativelynon-rotatably around its axis, a sub-speed change unit 40 locateddownstream of the propeller shaft 220 with respect to the powertransmission direction, and a differential gear unit 50 for transmittingpower from the sub-speed change unit 40 to a pair of main transmissionshafts (a pair of rear axles in this embodiment), enabling them to berotated at different speeds.

As best illustrated in FIG. 2, the propeller shaft 220 has a front endconnected to the motor shaft 210 in such a manner as to be relativelynon-rotatably around its axis and a rear end supported by the centerplate 18. Preferably, the hollow body portion 121 of the intermediatehousing 120 is integrally formed with a bearing wall 123 that extendsradially inwardly from an inner circumference of the top wall 121 a, sothat a center portion of the propeller shaft 220 can bebearing-supported by the bearing wall 123. With the above arrangement,it is possible to support the propeller shaft 220 in a secure manner.

The sub-speed change unit 40 is accommodated in the transmission case130, as illustrated in FIG. 2. Now, the description will be made for thestructure of the transmission case 130. FIG. 10 is a cross sectionalview taken along a line X-X in FIG. 2.

As illustrated in FIGS. 2 and 10, the transmission case 130 has a bodyportion 131 having a front opening 130 a and a rear opening 130 b. Thebody portion has a bottom wall 131 a extending along the vehiclelongitudinal axis, a pair of lateral walls 131 b extending upwardly fromthe opposite sides of the bottom wall 131 a with respect to the vehiclewidthwise direction, a first intermediate wall 131 c extending upwardlyfrom an inner circumference of the bottom wall 131 a in such a manner asto divide an inner space defined by the bottom wall 131 a and the pairof side walls 131 b into a front section and a rear section, and asecond intermediate wall 131 d located rearward of the firstintermediate wall 131 c and extending upwardly from the innercircumference of the bottom wall 131 a in such a manner as to furtherdivide the rear section of the aforesaid inner space into a front partand a second part.

The body portion 131 has a front end, to which the center plate 18 isconnected to cover the front opening 130 a (see FIGS. 2 and 9), and arear end, to which a rear plate 19 is connected to seal the rear opening130 b in a liquid tight manner (see FIG. 2).

Specifically, the transmission case 130 provides a front chamber 130Fbetween the first intermediate wall 131 c and the center plate 18, anintermediate chamber 130M between the first intermediate wall 131 c andthe second intermediate wall 131 d, and a rear chamber 130R between thesecond intermediate wall 131 d and the rear plate 19. An upper opening130 c is formed in an upper part of the body portion 131 (see FIG. 2),and sealed by a hydraulic lift case 20 (see FIG. 1).

The sub-speed change unit 40 is accommodated in the front chamber 130Fof the transmission case 130. Specifically, as best illustrated in FIG.9, the sub-speed change unit 40 includes a driving shaft 401 operativelyconnected to the propeller shaft 220, a speed change shaft 403 locatedparallel to the driving shaft 401, a speed change device 420 forstepwisely changing the speed between the driving shaft 401 and thespeed change shaft 403, a speed change operation device 470 foroperating the speed change device 420.

The driving shaft 401 has a front end supported by the center plate 18and a rear end supported by the first intermediate wall 131 c. Thedriving shaft 401 is connected to a connecting shaft 402 which isconnected to the propeller shaft 220 in such a manner as to benon-rotatably around its axis, via a suitable power transmittingmechanism.

The speed change shaft 403 has a front end supported by the center plate18 and a rear end supported by the first intermediate wall 131 c. Thefront end of the speed change shaft 403 extends forward through thecenter plate 18 to have a front extension that forms a drive poweroutput member for outputting drive power to a sub axle 240 (a front axlein this embodiment). The rear end of the speed change shaft 403 extendsrearward through the first intermediate wall 131 c into the intermediatechamber 130M to have a rear extension operatively connected to thedifferential gear unit 50.

In this embodiment, as the speed change device 420, a mesh device thatenables power transmission at three speed stages is employed.Specifically, as best illustrated in FIG. 9, the mesh device 420includes a low-speed drive gear 421L, a medium-speed drive gear 421M anda high-speed drive gear 421H relatively non-rotatably supported on thedrive shaft 402, a low-speed driven gear 422L, a medium-speed drivengear 422M and a high-speed driven gear 422H relatively rotatablysupported on the speed change shaft 403 and held respectively in meshedengagement with the low-speed drive gear 421L, the medium-speed drivegear 421M and the high-speed drive gear 421H, a first clutch hub 423located between the low-speed driven gear 422L and the medium-speeddriven gear 422M and relatively non-rotatably supported on the speedchange shaft 403, a first sleeve 424 being capable of taking a low-speedposition enabling the low-speed driven gear 422L to be connected to thefirst clutch hub 423, a medium-speed position enabling the medium-speeddriven gear 422M to be connected to the first clutch hub 423 and aneutral position enabling the low-speed driven gear 422L and themedium-speed driven gear 422M to be disconnected from the first clutchhub 423, a second clutch hub 425 relatively non-rotatably supported onthe speed change shaft 403 at a position adjacent to the high-speeddriven gear 422H, and a second sleeve 426 being capable of taking ahigh-speed position enabling the high-speed driven gear 422H to beconnected to the second clutch hub 425 and a neutral position enablingthe high-speed driven gear 422H to be disconnected from the secondclutch hub 425.

According to the thus arranged mesh device 420, the first or secondsleeve 424, 426 is shifted so as to enable the low-speed, medium-speedor high-speed driven gear 422L, 422M, 422H to be selectively connectedto the first or second clutch hub 423, 425, so that the speed changeshaft 403 can be rotated at low speed, medium speed or high speed.

FIG. 11 is a cross sectional view taken along a line XI-XI in FIG. 10.

Now, the description will be made for the speed change operation device470. As illustrated in FIGS. 9-11, the sub-speed change operation device470 includes a speed change operation shaft 471 axially rotatablysupported by the pair of lateral walls 131 b of the transmission case130 so as to extend in the vehicle width direction within the frontchamber 130F of the transmission case 130, a speed change operation arm472 having a proximal end relatively non-rotatably supported on thespeed change operation shaft 471 so as to be located within the frontchamber 130F, a fork shaft 473 axially slidably supported by the centerplate 18 and the first intermediate wall 131 c so as to extend along thevehicle longitudinal axis within the front chamber 130F, first andsecond forks 474, 475 axially non-slidably supported on the fork shaft473, in which any one of the proximal ends of the first and second forks474, 475 is connected to a free end of the speed change operation arm472 (in this embodiment, the proximal end of the first fork 474 isconnected to the free end of the speed change operation arm 472), andfree ends of the first and second forks 474, 475 are respectivelyengaged with the first and second sleeves 424, 426, and a speed changeconnection arm 476 for operation of the speed change control shaft 471from the outside (see FIG. 1).

The thus arranged speed change operation device 470 is capable ofbringing the speed change device 420 into a low-speed state, a neutralstate, a medium-speed state and a high-speed state by rotating the speedchange operation shaft 471 around the axis, on the basis of operationfrom the outside by a speed change operation member 3 such as asub-speed change lever disposed around the driver seat. Preferably, thefork shaft 473 may be provided with a detent mechanism 478 forpreventing unintentional axial movement of the fork shaft 473 (see FIG.11).

FIG. 12 is a cross sectional view taken along a line XII-XII in FIG. 9.FIG. 13 is a development plan view of the transmission case in lateralcross section. As illustrated in FIG. 2, the differential gear unit 50is accommodated in the intermediate chamber 130M of the transmissioncase 130.

More specifically, the differential gear unit 50 includes a pair ofdifferential yoke shafts 51 (see FIG. 13) supported by the lateral walls131 b to respectively have inner ends located inward of the intermediatechamber 130M and outer ends located outward of the intermediate chamber130M, a pair of side bevel gears (not shown) relatively non-rotatablysupported on the inner ends of the pair of differential yoke shafts 51,a bevel gear (not shown) that is held in meshed engagement with the pairof side bevel gears and travels around the pair of differential yokeshafts 51 while being rotated around a pivotal shaft orthogonal to thepair of differential yoke shafts 51, and a ring gear 55 (see FIG. 9)connected to the pivotal shaft so as to keep the traveling of the bevelgear while permitting the rotation of the same.

The differential gear unit 50 is capable of transmitting drive power,which has been input from the rear end of the speed change shaft 403 tothe ring gear 55, to the pair of differential yoke shafts 51 (see FIGS.9 and 13). As seen in FIG. 13, the pair of differential yoke shafts 51are respectively and operatively connected to a pair of main-drive axles230 (a pair of rear axles in this embodiment) supported on the pair oflateral walls of the transmission case via a transmission gear 231.

The reference code 60 in FIG. 13 is a brake mechanism 60 placed in therunning-power transmission mechanism. The brake mechanism 60 is designedto be capable of directly or indirectly, and independently ordependently applying braking power to the pair of main-drive axles 230,to which drive power is transmitted from the power source, according tothe selected operation from the outside.

In this embodiment, the running-power transmission mechanism is furtherprovided with a sub-axle power take-off unit 250 for outputting drivepower to the sub axle 240 (the front axle in this embodiment).

As illustrated in FIG. 9, the sub-axle power take-off unit 250 includesa drive-side member 255 that is relatively non-rotatably mounted on thefront end of the speed change shaft 403 and has a spline on the outercircumference, a sub-axle drive shaft 260 (see FIG. 2) supported by theintermediate housing 120 so as to be coaxially aligned with the speedchange shaft 403, a driven-side member 265 that is relativelynon-rotatably supported on the sub-axle drive shaft 260 so as to belocated opposite to the drive-side member 255 and has a spline on theouter circumference, a sleeve 270 that is mounted on the drive-sidemember 255 and the driven-side member 265 and capable of taking anengaging position enabling connection between both the members 255, 265in a relatively non-rotatable manner and a shutdown position enablingshutdown of power transmission from the drive-side member 255 to thedriven-side member 265, and an operation mechanism 280 for operation ofthe sleeve 270.

As illustrated in FIG. 12, the operation mechanism 280 includes asub-axle operation shaft 281 relatively rotatably supported by theintermediate housing 120 so as to extend in the vehicle width direction,and a fork member 282 that has a proximal end relatively non-rotatablysupported on the sub-axle operation shaft 281 and a distal end arrangedto be engaged with the sleeve 270.

The sub-axle operation shaft 281 is located to have at least one endprotruding outward to have an outer extension, through which thesub-axle operation shaft 281 is rotated around the axis on the basis ofthe operation from the outside. In this embodiment, as illustrated inFIGS. 1 and 12, a proximal end of a sub-axle drive crank arm 285 isrelatively non-rotatably connected to the outer extension of thesub-axle operation shaft 281. The sub-axle drive crank arm 285 has afree end connected to a free end of a hydraulic piston 291, a proximalend of the hydraulic piston 291 being placed in a hydraulic cylinder 290for switching of the sub-axle drive.

With the above arrangement, the reciprocal motion of the hydraulicpiston 291 relative to the hydraulic cylinder 290 causes the rotation ofthe sub-axle operation shaft 281 around the axis, and hence enables thesleeve 270 to be positioned at an engaging position or release position.

Now, the description will be made for the PTO transmission mechanism.

As illustrated such as in FIGS. 2-4, and 9, the PTO transmissionmechanism includes the pump shaft 200 operatively connected to theengine 10 via the flywheel 15, the main shaft 150 connected to adownstream end of the pump shaft 200 in the power transmission directionin such a manner as to be relatively non-rotatable around the axis, aPTO drive shaft 160 connected to a downstream end of the main shaft 150in the power transmission direction in such a manner as to be relativelynon-rotatable around the axis, a PTO driven shaft 170 located downstreamof the PTO drive shaft 160 in the power transmission direction, amain-PTO clutch unit 70 for selectively performingpower-transmission/power-shutoff from the PTO drive shaft 160 to the PTOdriven shaft 170, a rear PTO shaft 180 relatively rotatably supported bythe second intermediate wall 131 d and the rear plate 19 so as to have afirst end outwardly extending, a mid PTO shaft 190 supported to have afirst end outwardly extending, and a PTO switch unit 80 for selectivelyperforming power-transmission/power-shutoff from the PTO driven shaft170 to the rear PTO shaft 180 and/or the mid PTO shaft 190.

The main shaft 150 extends into the intermediate housing 120 along thevehicle longitudinal axis, as illustrated in FIG. 2. Preferably, thebearing wall 123 of the intermediate housing 120 has a bearing hole forbearing-support of the main shaft 150, which enables secure support ofthe main shaft 150.

The PTO drive shaft 160 is rotatably supported by the center plate 18and the first intermediate wall 131 c, as illustrated in FIGS. 2 and 9.The PTO driven shaft 170 is rotatably supported by the secondintermediate wall 131 d and the rear plate 19 so as to be coaxiallyaligned with the PTO drive shaft 160.

FIGS. 14 and 15 are respectively circuit diagrams in one part andanother part of the vehicle 1, to which the frame structure 100 of thisembodiment has been applied.

The PTO clutch unit 70 is designed to perform power-transmission fromthe PTO drive shaft 160 to the PTO driven shaft 170 with bringingfriction plates into frictional engagement with each other by thehydraulic effect (see FIG. 15).

In this embodiment, the PTO transmission mechanism further includes aPTO brake unit 75 operable in association with the PTO clutch unit 70.The PTO brake unit 75 is designed not to apply brake power against thePTO driven shaft 170 when the PTO clutch unit 70 is in apower-transmitting state in which the PTO clutch unit 70 transmits drivepower from the PTO drive shaft 160 to the PTO driven shaft 170, and toapply brake power against the PTO driven shaft 170 when the PTO clutchunit 70 is in a power-shutoff state in which the PTO clutch unit 70shutoff drive power from the PTO drive shaft 160 to the PTO driven shaft170.

As best illustrated in FIG. 9, in this embodiment, the PTO switch unit80 includes a first transmission gear member 801 mounted on a portion ofthe PTO driven shaft 170 located within the rear chamber 130R, a secondgear member 802 relatively rotatably supported on the rear PTO shaft 180in meshed engagement with the first transmission gear member 801, a rearPTO sleeve 803 that is axially movable and relatively non-rotatable tothe rear PTO shaft 180 and is capable of taking an engaging positionenabling meshed engagement with internal threads formed on the secondgear member 802 and a release position releasing itself from meshedengagement with the internal threads, a third gear member 804 held inmeshed engagement with the second gear member 802, a first intermediateshaft 805 that relatively non-rotatably supports the third gear member804, a fourth gear member 806 held in meshed engagement with the thirdgear member 804, a second intermediate shaft 807 that is rotatablysupported by the second intermediate wall 131 d and the rear plate 19and relatively non-rotatably supports the fourth gear member 806, a midPTO transmission shaft 808 located coaxial with the second intermediateshaft 807, a mid PTO sleeve 809 that is axially movably supported by themid PTO transmission shaft 808 and the second intermediate shaft 807 andis capable of taking an engaging position enabling connection of boththe shafts 808, 807 together in a relatively axially non-rotatablemanner and a release position enabling both the shafts 808, 807 to berelatively axially movable to each other, a mid PTO case 820 (see FIG.10) that is separably connected to the transmission case 130 andsupports the mid PTO shaft 190, and a gear train 825 (see FIG. 13) thatconnects the mid PTO transmission shaft 808 and the mid PTO shaft 190together and is supported by the mid PTO case 820. The rear PTO sleeve803 and the mid PTO sleeve 809 are operated by a suitable operationmechanism (not shown).

As illustrated in FIG. 1, the vehicle of this embodiment is equippedwith a mower device 9 under the frame structure 100 to be operativelydriven by the mid PTO shaft 190.

More preferably, the PTO switch unit 80 is provided with a PTO outputdetection mechanism 88 for detecting the output status of each of therear PTO shaft 180 and the mid PTO shaft 190. The PTO output detectionmechanism 88 has first and second switches 881, 882 to be turned on andoff according to the axial position of a PTO fork shaft.

Now, the description will be made for a hydraulic mechanism 90 of thevehicle in this embodiment. The hydraulic mechanism 90 includes a tank901 for storing hydraulic fluid, and first and second hydraulic pumps903, 904 for respectively sucking stored hydraulic fluid from the tank901 through a filter 902.

In this embodiment, at least a portion of the inner space of the framestructure 100 is used as the tank 901. That is, the flywheel housing110, the intermediate housing 120 and the transmission case 130 formaccommodating spaces for various transmission mechanisms, as well asconstituting a portion of the chassis, in which at least a portion ofthe inner space forms a hydraulic fluid reservoir space.

Now, the description will be made in detail for the hydraulic fluidreservoir space of the frame structure 100. As described above, theframe structure 100 is designed so that the inner spaces of theintermediate housing 120 is utilized as a fluid chamber, and theflywheel accommodating space (a space other than the space occupied bythe HST unit 30) of the flywheel housing 110 is utilized as a drychamber.

In addition to the above arrangement, as illustrated in FIG. 9, thecenter plate 18, which is interposed between the intermediate housing120 and the transmission case 130, has fluid communication ports 18 a onits lower side. The rear opening of the transmission case 130 is sealedby the rear plate 19 in a liquid tight manner, as described above. Withthis arrangement, the frame structure 100 of this embodiment makes itpossible to utilize the inner spaces of the intermediate housing 120 andthe transmission case 130 as the fluid reservoir space.

Further, the frame structure 100 is designed to make it possible to gethydraulic fluid out of the fluid reservoir space via the filter 902.

Specifically, the frame structure 100 has a partition wall 101. Thepartition wall 101 is designed to divide the fluid reservoir space intoa filter accommodating portion 100 a for accommodating the filter 902and a main portion 100 b other than the filter accommodating portion 100a.

In this embodiment, as illustrated in FIG. 10, the partition wall 101 isprovided on the transmission case 130. Specifically, the transmissioncase 130 has a bulge 135 that extends in the vehicle width directionover a region of the transmission case 130 from the front end, which endfacing the rear end of the intermediate housing 120 through the centerplate 18, rearward to a portion with a predetermined distance. The bulge135 forms the filter accommodating portion 100 a.

In the transmission case 130, the partition wall 101 extends from theinner surface of one of the pair of lateral walls 131 b, on which thebulge 135 is formed, towards the lateral center of the transmission case130. The inner space of the bulge 135 is divided from the other portionby the partition wall 101.

More specifically, the partition wall 101 has a communication port 102for communication between the filter accommodating portion 100 a and themain portion 100 b in a lower region of the fluid reservoir space. Thatis, the partition wall 101 divides the filter accommodating portion 100a from the main portion 100 b in such a manner as to allow fluidcommunication only in the lower region.

The frame structure of this embodiment is capable of securely gettinghydraulic fluid out of the fluid reservoir space without fluidrunning-out, while keeping the amount of hydraulic fluid stored thereinas low as possible without increasing a height from ground.

That is, the fluid stored in the fluid reservoir space causes a dragresistance in various transmission mechanisms placed inside of the framestructure 100. Accordingly, it is preferable to reduce the amount offluid stored in the fluid reservoir space in light of the powertransmission efficiency. On the other hand, excessive reduction ofhydraulic fluid in the fluid reservoir space may cause fluid running-outduring the fluid is drawn out. Particularly, when the vehicle tilts dueto such as running up or down a slope, the surface level of store fluidis changed. As a result, air may be drawn into a hydraulic circuit.

The frame structure 100 of this embodiment is designed so that thepartition wall 101 allows the filter accommodating portion 100 a to becommunicated with the main portion only in the lower region of the fluidreservoir space. With this arrangement, it is possible to keep variationin the surface level of hydraulic fluid in the filter accommodatingportion 100 a, which is caused by variation in vehicle's posture or thelike, as low as possible. Accordingly, the amount of hydraulic fluid inthe fluid reservoir space can be limited, thereby preventingdeterioration in power transmission efficiency, while effectivelypreventing running-out of hydraulic fluid sucked through the filter 902.

Preferably, the partition wall 101 is located to have the communicationport 102 positioned substantially at the vehicle lateral center. Withthis arrangement, it is possible to limit variation in surface level ofhydraulic fluid in the filter accommodating portion 100 a when thevehicle has tilted rightward or leftward. In this embodiment, asillustrated in FIG. 10, the partition wall 101 has a horizontal portion101 a extending substantially horizontally from the lateral wall 131 bof the transmission case 130 substantially to the lateral center of theframe structure 100, and a vertical portion 101 b extending from a freeend of the horizontal portion 101 a substantially downward, in which thecommunication port 102 defined by a free end of the vertical portion 101b and an inner surface of the bottom wall 131 a of the transmission case130 is positioned substantially at the vehicle lateral center.

More preferably, the partition wall 101 is located to have thecommunication port 102 positioned substantially at the center of thefluid reservoir space with respect to the vehicle longitudinaldirection. With this arrangement, it is possible to effectively limitvariation in surface level of hydraulic fluid within the filteraccommodating portion 101 a when the vehicle has tilted forward orrearward. In this embodiment, as described above, the inner spaces ofthe intermediate housing 120 and the transmission case 130 together forma fluid reservoir space. Therefore, the partition wall 101 is formednear the front end of the transmission case 130.

More preferably, as illustrated in FIGS. 9 and 10, an oil heater 105 isprovided near the communication port 102 so as to effectively preventdeterioration in viscosity of hydraulic fluid during cold season. Thatis, hydraulic fluid sucked through the filter 902 is drawn into thefilter accommodating portion 100 a through the communication port 102from the main portion 100 b. Thus, the oil heater 105 provided near thecommunication hole 102 can efficiently heat hydraulic fluid when it isdrawn out of the fluid reservoir space for use.

In this embodiment, as illustrated in such as FIG. 9, a downward bulge122 is formed near the rear end of the intermediate housing 120 and theoil heater 105 is introduced through the front side of the downwardbulge 122 and detachably installed in place. A reference code 18 b inFIG. 9 represents a passing hole formed in the center plate 18, throughwhich the oil heater passes.

In this embodiment, the frame structure 100 is made up of three units,namely the flywheel housing 110, the intermediate housing 120 and thetransmission case 130. In this regard, it is to be noted that the effectproduced by providing the partition wall 101 is not limited to thearrangement of this embodiment. That is, it is possible to apply thepartition wall 101 to a frame structure made up of a single unit, twounits or the like, as far as such unit(s) are arranged from one side toanother side along the vehicle longitudinal axis and can utilize atleast a portion of the inner space defined by the unit(s) as a hydraulicfluid reservoir space.

The hydraulic mechanism 90 further includes a hydraulic controlmechanism 905 for controlling the HST unit 30 (see FIG. 14), to whichhydraulic fluid sucked from the fluid reservoir space through the filter902 by the first hydraulic pump 903 is supplied. In this embodiment, apower-steering hydraulic circuit 905 is interposed between the firsthydraulic pump 903 and the hydraulic control mechanism 950 so as toutilize pressurized fluid from the first hydraulic pump as powersteering hydraulic fluid.

In this embodiment, the hydraulic control mechanism 950 has a hydrauliccontrol valve 950V which is connected to a side wall of the intermediatehousing 120, as illustrated in FIGS. 4 and 7.

The hydraulic control valve 950V has a main line 951 which has a firstend and a second end forming an inlet port 951(I) and an outlet port951(O) respectively, a line filter 912 disposed in the main line 951, acharge oil supply line 953 which has a first end communicated with themain line 951 at a second side of the line filer 912, a first supplyline 954 a and a second supply line 954 b, a relief line 957 which has afirst end communicated with the main line 951 and a second end openingto the inner space of the intermediate housing 120 so as to form a drainport 957(D), a relief valve 958 which is disposed in the relief line 957so as to set a pressure of the main line 951 to the predeterminedpressure, first and second switch valves 955 a and 955 b which havefirst side communicated with second ends of the first and second supplylines 954 a and 954 b respectively, first and secondsupplying/discharging lines 956 a and 956 b which have first endscommunicated with the second sides of the first and second switch valves955 a and 955 b respectively, and first and second discharge lines 959 aand 959 b which have first ends communicated with the first side of thefirst and second switch valves 955 a and 955 b respectively and secondends communicated with the drain port 957(D).

As illustrated in FIGS. 4, 5, 7 and 8, the second end of the charge oilsupply line 953 is in communication with a charge line 386 formed in thecenter section 380 through an appropriate oil conduit (oil passage 981formed in the intermediate housing 120 in this embodiment) provided inthe intermediate housing.

More specifically, as illustrated in FIG. 8, the charge line 386 of thecenter section 380 includes a bypass line 386 a which brings the pair ofoil passages 386 into communication with each other, a first charge line386 b whose first end is in communication with the bypass line 386 a andwhose second end is opened from an outer surface of the center section380, a second charge line 386 c whose first end is in communication withthe oil passage 981 and whose second end is opened from the outersurface of the center section 380, and a charge conduit 386 d whichbring the second ends of the first charge line 386 b and the secondcharge line 386 c into communication with each other.

On the other hand, the second ends of the first supplying/dischargingline 956 a and second supply line 956 b are brought into communicationwith the hydraulic operation device 315 through appropriate oilconduits. The hydraulic operation device 315 controls the slantingposition of the output adjusting member 313. Now, the description willbe made for the hydraulic operation device 315.

As illustrated in FIGS. 4 and 6, the hydraulic operation device 315includes a hydraulic cylinder 316, and a hydraulic piston 317 which isslidably accommodated in the hydraulic cylinder 316 such that the innerspace of the hydraulic cylinder 316 can be liquid-tightly separated intoa first hydraulic chamber 316(1) and a second hydraulic chamber 316(2).The hydraulic operation device 315 also includes a connecting member 318which connects the hydraulic piston 317 and the output adjusting member313 such that the output adjusting member 313 can slant in response tothe sliding operation of the hydraulic piston 317.

In this embodiment, the hydraulic cylinder 316 comprises a through hole316 a formed in the pump case 301 and a pair of lid members 316 b whichclose both end openings of the through hole 316 a.

The first supplying/discharging line 956 a is in communication with thefirst chamber 316(1) of the hydraulic cylinder 316 through anappropriate oil conduit.

In this embodiment, the first supplying/discharging line 956 a is incommunication with the first chamber 316(1) through a first conduit 982a, a communication passage 982 b and a second conduit 982 c. The firstconduit 982 a is disposed within the intermediate housing 120 so as tohave a first end communicated with the first supplying/discharging line956 a and a second end opened from the support surface 125 b of theintermediate housing 120. The communication passage 982 b is formed inthe center section 380 so as to have a first end which is opened fromits surface opposed to the support surface 125 b to communicate with thefirst conduit 982 a, and a second end which is opened from its surfaceopposite from the opposed surface. The second conduit 982 c is disposedin the flywheel housing 110 so as to have a first end communicated withthe second end of the communication passage 982 b and a second endcommunicated with the first chamber 316(1).

Similarly, the second supplying/discharging line 956 b is incommunication with the second chamber 316(2) of the hydraulic cylinder316 through an appropriate oil conduit.

In this embodiment, the second supplying/discharging line 956 b is incommunication with the second chamber 316(2) through a first conduit 983a, a communication passage 983 b and a second conduit 983 c. The firstconduit 983 a is disposed within the intermediate housing 120 so as tohave a first end communicated with the second supplying/discharging line956 b and a second end opened from the support surface 125 b of theintermediate housing 120. The communication passage 983 b is formed inthe center section 380 so as to have a first end which is opened fromits surface opposed to the support surface 125 b to communicate with thefirst conduit 983 a, and a second end which is opened from its surfaceopposite from the opposed surface. The second conduit 983 c is disposedin the flywheel housing 110 so as to have a first end communicated withthe second end of the communication passage 983 b, and a second endcommunicated with the second chamber 316(2).

In this embodiment, the first and second switch valves 955 a and 955 bwhich control the supply and discharge operations of hydraulic oil toand from the hydraulic operation device 315 are provided in the HSThydraulic control valve 950V mounted on an outer wall surface (outerwall surface of the intermediate housing 120 in this embodiment) of theframe structure 100.

Therefore, control signal wires for the first and second switch valves955 a and 955 b need not be routed into the frame structure, and it ispossible to simplify the wiring structure between the first and secondswitch valves 955 a, 955 b and the HST operating member 2 (see FIG. 1)disposed in the vicinity of the driver's seat, and it is possible tofacilitate the piping operation and maintenance operation.

As illustrated in FIG. 15, the outlet port 951(O) of the main line 951is in communication with the PTO valve 93 (see FIG. 1). The PTO valve 93controls the supply and discharge operation of hydraulic oil to and fromthe PTO clutch unit 70 and the PTO brake unit 75 through a conduit 921.The PTO valve 93 also controls the supply and discharge operation ofhydraulic oil to and from the auxiliary axle driving switch hydrauliccylinder 290.

The PTO valve 93 includes a PTO clutch line 931 and a switch line 932for the auxiliary driving axle which are in communication with theconduit 921, and solenoid valves 933 and 934 inserted into the lines 931and 932, respectively.

The hydraulic mechanism 90 includes a hydraulic oil supply valve 907 fora hydraulic lift, to which hydraulic oil is supplied from the secondhydraulic pump 904 (see FIG. 15).

The hydraulic mechanism 90 also includes a PTO lubricating line 941. ThePTO lubricating line 941 supplies relief oil from the hydraulic lifthydraulic oil supply valve 907 to the PTO clutch unit 70 and the PTObrake unit 75 as lubricant oil.

As illustrated in FIG. 9, the PTO lubricating line 941 is incommunication with a lubricating oil path formed in the PTO drivingshaft 160 through an oil path 942 formed in a first intermediate wall131 c of the transmission case 130.

In this embodiment, two hydraulic pumps (the first and second hydraulicpumps 903, 904) are provided in order to address excessive load appliedto a single hydraulic pump. That is, the number of hydraulic pumps areproperly set according to the installed hydraulic circuits. It is amatter of course that various hydraulic circuits provided in thisembodiment are properly subjected to omission, modification or additionaccording to the specification of a vehicle.

This specification is by no means intended to restrict the presentinvention to the preferred embodiments set forth therein. Variousmodifications to the frame structure, as well as the brake mechanism asdescribed herein, may be made by those skilled in the art withoutdeparting from the spirit and scope of the present invention as definedin the appended claims.

1. A frame structure of a vehicle comprising a flywheel housing, anintermediate housing and a transmission case that are connected to eachother along a longitudinal axis of the vehicle to constitute a vehicleframe with an inner space for accommodating a running-power transmissionpath for transmitting power from an engine to sub drive wheels and maindrive wheels respectively located closer to a first end and a second endalong the longitudinal axis of the vehicle via a HST unit: wherein theflywheel housing has a first end and a second end along the longitudinalaxis of the vehicle, the first end being connected to the engine, thesecond end being provided with an opening; the intermediate housing is ahollow shape having a first end and a second end along the longitudinalaxis of the vehicle, the first end of the intermediate housing beingprovided with an abutting surface located opposite to the second end ofthe flywheel housing, a support surface located radially inward of theabutting surface so as to support the HST unit and a first-end openinglocated radially inward of the support surface, the second end of theintermediate housing being provided with a second-end opening, theabutting surface and the support surface being located in thelongitudinal axis of the vehicle so that at least a portion of the HSTunit is accommodated within the flywheel housing; a sub-axle drive shaftfor transmitting driving power toward the sub drive wheels is disposedat lower portions within the flywheel housing and the intermediatehousing so as to extend along the longitudinal axis of the vehicle; theHST unit includes a pump shaft operatively connected to the engine, ahydraulic pump unit driven by the pump shaft, a hydraulic motor unitthat non-stepwisely changes a driving force from the engine incooperation with the hydraulic pump unit, a motor shaft rotated by thehydraulic motor unit, and a center section forming a hydraulic circuitfor fluidly communicating the hydraulic pump unit and the hydraulicmotor unit; the center section has a first side in the longitudinal axisof the vehicle forming a pump support surface which supports thehydraulic pump unit, and a second side in the longitudinal axis of thevehicle forming a motor support surface which supports the hydraulicmotor unit; the pump shaft is disposed upwardly than the motor shaft,and extends along the longitudinal axis of the vehicle such that itsfirst end extends within the flywheel housing so as to be operativelyconnected to the engine and its second end extends toward the second endof the vehicle through the center section; and the motor shaft extendsalong the longitudinal axis of the vehicle within the intermediatehousing such that its second end extends toward the second end of thevehicle, and is displaced to one side in the vehicle width directionfrom a line connecting the sub-axle drive shaft and the pump shaft.
 2. Aframe structure of a vehicle according to claim 1, wherein: theintermediate housing has a hollow body portion and a flange portionlocated closer to a first end along the longitudinal axis of the hollowbody portion, the flange portion forming the first-end opening at aradially center; the flange portion has the abutting surface and thesupport surface located radially inward of the abutting surface so as tosupport the center section of the HST unit; the center section isconnected with the support surface of the flange portion so as to sealan inner space of the flywheel housing against an inner space of theintermediate housing in a liquid tight manner, while the sub-axle driveshaft is extends from the inner space of the intermediate housing intothe inner space of the flywheel housing through a portion between theabutting surface and the support surface in a radial direction in aliquid tight manner.
 3. A frame structure of a vehicle comprising aflywheel housing, an intermediate housing and a transmission case thatare connected to each other along a longitudinal axis of the vehicle toconstitute a vehicle frame with an inner space for accommodating arunning-power transmission path for transmitting power from an engine todrive wheels via a HST unit: wherein the flywheel housing has a firstend and a second end along the longitudinal axis of the vehicle, thefirst end being connected to the engine, the second end being providedwith an opening; the intermediate housing is a hollow shape having afirst end and a second end along the longitudinal axis of the vehicle,the first end of the intermediate housing being provided with anabutting surface located opposite to the second end of the flywheelhousing, a support surface located radially inward of the abuttingsurface so as to support the HST unit and a first-end opening locatedradially inward of the support surface, the second end of theintermediate housing being provided with a second-end opening, theabutting surface and the support surface being located in thelongitudinal axis of the vehicle so that at least a portion of the HSTunit is accommodated within the flywheel housing; the HST unit includesa pump shaft operatively connected to the engine, a variabledisplacement type hydraulic pump unit driven by the pump shaft andhaving a hydraulic operation type output adjusting member, a hydraulicmotor unit that non-stepwisely changes a driving force from the enginein cooperation with the hydraulic pump unit, a motor shaft rotated bythe hydraulic motor unit, and a center section forming a hydrauliccircuit for fluidly communicating the hydraulic pump unit and thehydraulic motor unit; the center section has a first side in thelongitudinal axis of the vehicle forming a pump support surface whichsupports the hydraulic pump unit, and a second side in the longitudinalaxis of the vehicle forming a motor support surface which supports thehydraulic motor unit; and the hydraulic operation type output adjustingmember is operated by hydraulic oil of which a switch valve in a valveunit mounted on an outer wall of the intermediate housing controls thesupply and discharge, and which flows in hydraulic lines within theintermediate housing and the flywheel housing.